Plant Cells and Growth
Plant form and function is ruled by cells
- Plant cells range from 10-100um in length
- Cell walls maintain physical framework
- maintain cell turgidity
- Root cells uptake & transport H2O
- Leaf cells are specialized for photosynthesis
- Cells of flowers control reproduction
- produce pigments and nectar
Plant cell walls
- Mostly made of cellulose
- strength and protection of protoplast
- chains of cellulose molecules = fibrils
- Metabolism does occur (not inert)
- Consists or 1 or 2 layers
- primary wall (1st layer) = cellulose fibers
- secondary wall (internal) = lignin
- Sticky layer (lamella) between walls
- made of pectin (jelly!)
Support or water conducting cells have secondary walls
Cellulose and lignin extremely abudant on Earth
Why dont plants have strong bones made of Calcium?
- Animals with shells use calcium carbonate
- carbonate comes from seawater, so pH not affected
- Animals with internal skeleton use calcium phosphate
- cant handle carbonate
- phosphate has little effect on cell acidity
- Plants must also be careful with Calcium and its salts
- plants need phosphate badly
- lignin and cellulose are inert
- lignin and cellulose carbs from photosynthesis
Plant cells are not solid structures (cytoplasm channels)
Plant cells are not quite individuals
- Plasmodesmata diminish individuality of cells
- symplast: interconnections of protoplasm
- living region, transport & communication
- Cell walls do separate cells, just not cleanly
- lots of intercellular air spaces (@ corners)
- apoplast: cells walls + intercellular spaces
- gas diffusion occurs via apoplast
- water through cell wall via capillary action
Plant cell membrane structure fits fluid mosaic model
- Membrane covers the surface of the protoplasm
- Molecular pumps transport molecules in and out
- Impermeable to bad stuff, permeable to beneficial stuff
Anatomy of a plant cell
- Virtually all plant cells, although diverse, have conserved organelles
- roots, wood, barks, leaves, flowers
- certain organelles can become modified
- Contain protoplasm: water + proteins, lipids & nucleic acids
- Nucleus, ribosomes and endoplasmic reticulum
- Golgi apparatus: transport, modify, and package proteins & lipids for delivery
- Peroxisomes: organelle that produces or uses peroxide
- detoxify product of photosynthesis
Plastids: membrane bound organelles in plants & algae
- Chloroplast: double membrane organelles in leaf cells
- key for photosynthesis
- interesting evolutionary history
- Leucoplast: colorless organelles storing starch
- Chromoplasts: organelles containing pigments for colored plant parts
Central vacuole makes up most volume in mature cells
New cells orginate from meristems
- All plants are multicellular with active regions of cell division
- cells mostly divide my mitosis
- meiosis in parts of reproductive cycle
- Growth is localized in the active regions: meristems
- meristem cells are undifferentiated
- Apical meristems: @ tips of roots and stems
- cell division propels tissues ‘out’
- primary growth of leaves, stem & roots
New cells orginate from meristems
- All plants are multicellular with active regions of cell division
- cells mostly divide my mitosis
- meiosis in parts of reproductive cycle
- Growth is localized in the active regions: meristems
- meristem cells are undifferentiated
- Lateral meristems: secondary growth
- cell division adds diameter
- support, xylem, phloem cells
- tissues called ‘cambium’
Cancerous growth in plants?
- Release of cell cycle arrest in humans can be fatal
- cigarette smoke can cause lung cancer
- UV triggers skin cancer
- Galls: abnormal growth causes by reaction to insects/microbes
- Irregular cell growth in plants not a big deal
- cells cannot migrate in plants
- no single plant organ is indispensable
